Suppose a person wants to anonymously order an NIC via postal mail. That way the MAC address is not tied to their name. I understand that alternatives exists, like Walking into a store and buying an NIC with cash, but I am still wondering if it's possible for other reasons. Maybe a physical book on security exploits is unavailable at a local bookstore or electronic format. The security professional might not want to create a record that ties her to the book.

Do all PO Boxes require identification? As far as I know, prepaid debit cards can no longer be purchased without revealing personal information. Are there any exceptions to that or alternatives?

Edit:
There are private companies that accept mail and forward it to a new address. With anonymous purchases these private services and using multiple private PO Boxes together, it could be interesting.